Efficient capture and removal of carbon dioxide from flue gas is an essential technology for the development of more environmentally acceptable fossil fuel-based energy production systems, particularly for cleaner coal-based energy production. Several existing carbon dioxide capture processes utilize a vacuum to pull CO2 across a membrane or from a solvent, which imparts a high energy cost for the CO2 removal. Others utilize a temperature elevation to drive CO2 from the solvent. CO2 capture is the single most costly step in greenhouse gas (GHG) control. Capture of CO2 from pulverized coal power plant flue gas is crucial for improving the environmental profile of the power generation industry. This represents a principal hurdle for commercializing new fossil fuel-based energy generation technologies in the present, CO2 constrained world. Key factors in developing new CO2 capture technologies include cost efficiency, and low capture energy consumption, preferably suitable for use with the relatively low pressure and dilute characteristics of flue gas feed streams. Improved CO2 capture, driven by the pH dependent equilibrium between gaseous CO2 and bicarbonate ion, provides a promising avenue for new capture technologies.
Electrodeionization (EDI), also known as electrochemical ion-exchange or continuous deionization, is an advanced ion-exchange technology that combines the advantages of ion-exchange column techniques and electrodialysis. In an EDI process, ion exchange resins are sequestered in dilute compartments to increase ionic conductivity, so that even with very dilute ionic feeds (e.g., 10−5 N), a stable operation with higher flux and lower energy consumption than electrodialysis becomes possible. EDI technology is presently used to make deionized water for boiler feed and high purity and industrial water applications. A particularly useful variant of EDI (referred to herein as “resin-wafer EDI”) utilizes porous solid ion exchange resin wafers in place of the traditional column or bed of ion exchange beads. There are a number of known EDI apparatus and processes, some of which are described in patent publications and/or issued patents filed on behalf of Argonne National Laboratory (ANL) such as, for example, U.S. Pat. Nos. 6,797,140, 6,495,014, 7,306,934, 7,141,154, U.S. Patent Publication No. 2008/0187902, U.S. Pat. Nos. 7,452,920, and 7,507,318. The entire disclosure of each of the foregoing patents and publications is incorporated herein by reference.
U.S. Patent Publication No. 2010/0300894 to Lin et al., which is incorporated herein by reference in its entirety, describes a resin-wafer EDI apparatus that facilitates removal of CO2 from a gas stream at a significantly decreased energy consumption compared to the currently used technologies. This apparatus comprises cathode and anode electrodes separated by a plurality of porous solid ion exchange resin wafers, which when in use are filled with an aqueous fluid. The plurality of wafers comprises one or more basic wafers arranged in a stack between the cathode and the anode. The wafers, anode, and cathode are interleaved with ion exchange membranes. Each basic wafer comprises a porous basic ion exchange medium. Each basic wafer is adapted to (a) introduce a CO2-containing gas into an aqueous fluid within the basic ion exchange medium to convert CO2 from the gas into bicarbonate ion, and (b) vent a CO2-depleted gas therefrom. In use, CO2 is converted to bicarbonate in the fluid within the wafer under the basic conditions of the basic ion exchange medium. The bicarbonate-containing fluid can then be transported out of the apparatus as a concentrated bicarbonate ion solution.
One drawback of the EDI design provided by US2010/033894 is that CO2 gas entering the wafer sometimes can channel, leading to uneven distribution of the gas in the wafer. This channeling, when it occurs, reduces the efficiency of CO2 removal. Consequently, there is a need for an improved EDI design that ameliorates CO2 gas channeling. The present invention addresses this need.